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Copied and pasted from the red diffs:
https://github.com/xataio/pgroll/pull/773/files

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…one to the table (#788)

The following migration was failing due to several reasons:

```json
{
  "operations": [
    {
      "create_table": {
        "name": "users",
        "columns": [
          {
            "name": "id",
            "type": "uuid",
            "pk": true
          }
        ]
      }
    },
    {
      "add_column": {
        "table": "users",
        "column": {
          "name": "name",
          "type": "text",
          "nullable": true
        }
      }
    },
    {
      "create_constraint": {
        "table": "users",
        "columns": [
          "name"
        ],
        "type": "unique",
        "name": "my_custom_name",
        "up": {
          "name": "name"
        },
        "down": {
          "name": "name"
        }
      }
    }
  ]
}
```

This PR fixes the first problem with the migration. The first problem is
when `pgroll` adds the new column with the temporary name to the table
schema it lacks all column attributes. Thus, if a later operation tries
to duplicate this duplicated column it fails because we do not know the
type of the column, the default value, etc. The SQL statement generated
has a syntax error because of the lack of information:

```
Failed to start migration: unable to execute start operation: failed to duplicate column: pq: syntax error at or near ","
```

When a table was added, `pgroll` did not store all required column
metadata. Default values and comments were missing from columns. So when
`pgroll` tried to duplicate the column, these got lost.

Example to reproduce the issue:
```json
{
    "operations": [
        {
            "create_table": {
                "name": "useres",
                "comment": "my_comment",
                "columns": [
                    {
                        "name": "id",
                        "type": "uuid",
                        "pk": true,
                        "nullable": false,
                        "default": "gen_random_uuid()",
                        "comment": "my_comment"
                    }
                ]
            }
        },
        {
            "create_constraint": {
                "table": "users",
                "columns": ["id"],
                "type": "unique",
                "name": "my_unique",
                "up": {
                    "id": "id"
                },
                "down": {
                    "id": "id"
                }
            }
        }
    ]
}
```